MONTPELIER — Telecommunications companies AT&T Mobility, Sprint and T-Mobile have agreed to stop charging customers for premium text messages, the unauthorized third-party charges that appear on cellphone bills, the state attorney general said.

Vermont is leading 45 states in trying to end the unauthorized billing practice, called cramming, Attorney General Bill Sorrell said late last week. The Federal Trade Commission defines cramming as when a company adds to a phone bill a charge for a service the customer didn’t order.

Sorrell said he was hopeful other carriers would soon follow the lead of the three companies he mentioned.

“We are pleased that AT&T, Sprint and T-Mobile have decided to stop the flow of money from the pockets of ordinary people to the bank accounts of scam artists,” he said.

Premium texts, which account for the majority of third-party charges on cellphones and for the overwhelming majority of cramming complaints, are part of messaging services offered by third-party providers for extra fees, such as voting during television reality shows and weather alerts. They have some benefits, such as for charitable giving and political donations, but they’re a major contributor to the cramming problem, Sorrell said.

T-Mobile said it will no longer allow third parties to bill customers for premium SMS but charitable text-to-give campaigns and political donations will be unaffected.

“At T-Mobile, our customers come first and we believe they should be treated fairly and not charged for unwanted services,” it said in an emailed statement. “Despite protections and processes put in place by T-Mobile and the industry, not all premium SMS vendors have acted responsibly.”

It said it would end most billing for PSMS as soon as possible and already had stopped business with one of the largest enablers of PSMS.

AT&T and Sprint didn’t immediately reply to emails seeking comment.

Another telecommunications company, Verizon Wireless, said it didn’t agree with all of the Vermont attorney general’s allegations but respected his efforts.

“For years, Verizon has been vigilant in protecting our customers from bad actors,” spokesman William B. Petersen said in an emailed statement.